The present invention relates to target tracking, and more particularly, to a method and apparatus for extracting robust, prominent features for target tracking.
Target tracking procedures are known in a variety of applications, including robot control, aircraft navigation systems, and missile guidance systems. Typically, an image is formed using an imaging system such as a forward looking infra-red camera, a radar system, or the like. This image contains a variable amount of noise which makes the task of target tracking more difficult.
Some of these prior art methods use two non-adaptive filters successively applied to increase the signal-to-noise ratio of the image and extract robust, prominent features from the scene. When two filters are utilized to extract robust features, the filters are chosen without regard to the characteristics of features present in the scene being imaged. In other words, there is no effort to select the filter parameters so they are optimal (i.e., result in the greatest increase of the signal-to-noise ratio) for a scene having particular characteristics. This may result in features having a signal-to-noise ratio which is lower than necessary. Additionally, the extracted features are likely to be unstable, that is, shift with time as an artifact of an inefficient filtering process, causing errors in the target tracking operations.
For example, U.S. Pat. No. 4,482,970 to Barry discloses a Boolean filtering method and apparatus for filtering noise in an image for target detection. Another method of discriminating noise from the target is disclosed in U.S. Pat. No. 4,956,792 to Sekine. However, in the systems of both of these patents, the same filter is used regardless of the target image. This can cause very unstable features to be selected for tracking.
Adaptive filters for use in aircraft navigation systems are also known. U.S. Pat. No. 4,654,811 to Jakubzick discloses an adaptive filter used on radar signals to reduce noise. The filter constant is changed depending on how far the aircraft is from the transmitting station. Thus, the Jakubzick system, varies the filter constant based upon distance information and not based on characteristics of the scene being imaged.